A definitive model of degenerative joint disease (primary osteoarthritis), directly analogous to the disease in humans, has been identified in the canine shoulder. Using this model the effects of the relative motion on the histology, histochemistry, and modulability of the two articular cartilage surfaces of the shoulder will be studied. An in-vivo method for determining the relative motion between the two articulating surfaces using an instrumented spatial linkage rigidly affixed to the bones has been developed. Using this method, the motion between the two articular surfaces will be determined for normal activities and compared with the histochemistry and histology of the articular cartilage. This data will also be correlated with the previously determined osteoarthritic model. Using this measurement method special activities will be devised and verified which will cause weight bearing contact over the entire articular surface of the humeral head. A group of dogs will then be trained, using these activities and, by comparing with a control group, the alteration to the histochemistry and histology of the articular cartilage will be evaluated to determine the effect of these special activities or exercises.